Many coals contain up to about 30 weight percent of moisture. This moisture not only does not add to the fuel value of the coal, but also is relatively expensive to transport.
Consequently, many processes have been developed to dry coal. Illustrative of these processes is the one disclosed in U.S. Pat. No. 4,324,544 of Blake, in which coal is dried in a fluidized bed in which the heat necessary for drying is provided by partial combustion of the coal in the bed. In the process of this Blake patent, after dried coal is withdrawn from a fluidized bed, it is maintained in a substantially inert off-gas atmosphere and thereafter cooled to a temperature below 140 degrees Fahrenheit. This inert atmosphere must be used because of pyrophoric nature of the coal makes it susceptible to spontaneous combustion.
Furthermore, the Blake patent teaches that its process should only be used with relatively fine coal, i.e., coal less than 8 mesh. At lines 30-35 of Column 4 of the Blake patent, it is disclosed that " . . . the above reaction rate constants were calculated from coal ground to below 8 mesh. The combustion rate appears to be limited by the amount of coal surface exposed to the fluidizing gas and, therefore, larger coal particles will probably oxidize less rapidly."
The coal produced by the processes of the prior art tends to suffer from several disadvantages. In the first place, the drying processes used to produce them often are reversible, and when the coal is allowed to stand in the presence of a moisture-laden atmosphere, it regains some or all of its initial water content. In the second place, the coal is often likely to undergo spontaneous combustion upon standing in air.
It is an object of this invention to provide a process for irreversibly removing moisture from coal which does not require substantial amounts of externally provided energy to drive it.
It is an object of this invention to provide a process for irreversibly removing moisture from coal which does not require one to reduce the particle size of the coal to 8 mesh prior to drying it.
It is another object of this invention to provide a process for producing coal which is not likely to undergo spontaneous combustion.
It is yet another object of this invention to provide a process for comminuting coal without using mechanical grinding means.
It is yet another object of this invention to provide a coal which, even after it is stored under ambient conditions for prolonged periods of time, has a relatively high heating value.
It is another object of this invention to provide an economical, relatively simple process for producing marketable coal from low rank coal.
It is yet another object of this invention to provide a process for producing marketable coal-liquid slurry from low rank coal.
It is yet another object of this invention to provide a novel coal-water slurry.